1. Field of the Invention
The present invention relates to a developing apparatus, and more particularly, to a developing apparatus for an image formation apparatus such as a copying unit, a printer, a facsimile unit, etc.
2. Description of the Prior Art
Conventionally, as a developing apparatus that is generally used for an image formation apparatus, there has been known a developing apparatus of the type that has a development roller, a developer restricting member, and a plurality of developer stirring shafts within the development casing.
As the developer stirring shafts disposed within the developing apparatus, there have been widely employed developer stirring shafts that have approximately elliptic stirring vanes (elliptic vanes) formed on the rotational axis or that have a screw-shaped spiral vane formed on the rotational axis.
For example, some developing apparatuses have a structure that a plurality of developer stirring shafts 1 are disposed adjacently in parallel with each other, each developer stirring shaft 1 having a plurality of elliptic vanes 2 installed on the slant at a predetermined angle on a rotational axis 3, as shown in FIGS. 1A and 1B.
Some other developing apparatuses have a structure that a plurality of developer stirring shafts are disposed adjacently in parallel with each other, each developer as stirring shaft 10 having a screw-shaped spiral vane 12 installed on a rotation axis 3, as shown in FIG. 2. Some other developing apparatuses have a structure that a plurality of a set of developer stirring shafts 20 and 21 are disposed adjacently in parallel with each other, the two developer stirring shafts 20 and 21 having spiral vanes 22 and 23 respectively having mutually different pitches. Further, some other developing apparatuses have a structure that a plurality of a set of developer stirring shafts are configured to oppose with each other so that pitches of spiral vanes of developer stirring shafts are shifted one-half pitch with respect to each other.
According to the structure of the developer stirring shafts having elliptic vanes formed on the rotational axis, the distribution of a developer becomes dense at portions where tip portions of the stirring vanes on the stirring shafts oppose with each other. However, at other portions, the shafts oppose with each other, and therefore, the distribution of the developer becomes coarse. As a result, uneven stirring of the developer tends to be emphasized.
Therefore, when the developer stirring shafts within the development casing have all the same shapes, the developer may be maldistributed at only one side within the development casing depending on the combination of the rotational direction. Thus, there has been a problem that the distribution of the developer is influenced by tilt of the development casing.
Further, as the developer conveying force is strong in the radial direction of the developer stirring shafts, some portion of the developer is supplied to the developing section without obtaining a sufficient stirring period within the development casing. Therefore, there has been a problem that this becomes a cause of a defect in the picture quality.
Further, when a plurality of developer stirring shafts 30 having the same shapes are disposed, each developer stirring shaft having elliptic vanes 32 formed in the same pitches, as shown in FIG. 4A and FIG. 4B, the tip portions of the elliptic vanes oppose with each other. At these portions where the tip portions opposes with each other, the developer is stirred strongly, and the conveying force of the developer becomes strong. On the other hand, at portions between the elliptic vanes, that is, at portions where the rotational shafts oppose with each other, the developer is stirred weakly, and the conveying force of the developer becomes weak.
Therefore, when the developer stirring shafts are disposed in such a way that the tip portions of the elliptic vanes coincide with each other between the adjacent developer stirring shafts, the stirring of the developer emphasizes the peak and bottom at the interface of the developer. As a result, uneven stirring of the developer tends become significant, due to occurrence of dense distribution portions and coarse distribution portions of the developer.
Further, when the machine is placed at a slanted position, the distribution of the developer becomes uneven and the developer is maldistributed at one end portion within the development casing. In this case, when the side at which the developer is shifted and the direction to which the developer is conveyed in the axial direction of the developer stirring shafts are the same, there is a problem that the maldistribution of the developer becomes more significant.
On the other hand, in the case of the structure of the developer stirring shafts that have screw-shaped spiral vanes installed on the rotation axes, the developer conveying force in the axial direction is secured. However, there has been a problem that the developer conveying force in the radial direction is inadequate. Further, since the developer conveying force in the axial direction is strong, stagnation of the developer and pressure increase thereof may be caused at the end portions in the conveying direction. Thus, the developer is subjected to a stress. Then, the developer may enter bearing portion which is disposed at the end portions of the conveying direction. As a result there has been a problem that the rotational shafts are blocked by the developer. Meanwhile, in the case of the structure of the developer stirring shafts that have spiral vanes of different pitches installed on the rotational axes, there has been a further problem that the shapes of the parts of the stirring shafts become complex.
In order to improve the stirring and the conveying performance of the developer in the developing apparatus having the above-described conventional structures, there have been the following proposals. In the case of the structure of the developer stirring shafts having elliptic vanes formed on the rotational axes, as disclosed in Japanese Patent Application Laid-open Hei 6 No. 89061 there has been proposed the following structure. That is to say, the developer stirring shafts have two spiral vanes of different pitches, with different external diameters, the external diameter becoming gradually larger toward one direction, or further having one stirring shafts installed with an angle.
Further, there has been proposed a structure of developer stirring shafts having a plurality of elliptic disks installed on the stirring shafts, with brushes provided uniformly between the disks, as disclosed in Japanese Patent Application Laid-open Hei 7 No. 168431.
Further, there has been proposed the following structure of developer stirring shafts, as disclosed in Japanese Patent Application Laid-open Hei 8 No. 95359. That is to say, developer stirring shafts are formed in a semi-cylindrical shape, with a plurality of plate-shaped outside-stirring vanes provided on the slant on the external periphery, and with a plurality of plate-shaped inside-stirring vanes provided on the slant on the inner periphery of the semi-cylinders, in the opposite direction to the slanting angle of the outside-stirring vanes. Further, there is provided a structure of these developer stirring shafts having their flat portions fixed to oppose with each other, and with the far end of each semi-cylinder cut open to communicate inside of each with.
On the other hand, in the case of the structure of the developer stirring shafts having screw-shaped vanes formed on the rotational axes, there has been proposed the following structure, as disclosed in Japanese Patent Application Laid-open Hei 9 No. 106154. The developer stirring shafts have a plurality of stirring vane shafts, with winding directions of spiral vanes at one side formed reversed to those of spiral vanes at the other side with the center portion of each rotational axis as the boundary. Based on this structure, the developer is stirred by combining an arrangement that the toner is conveyed from both sides to the center portion, and an arrangement that the toner is conveyed from the center to both sides, depending on the rotational directions of the developer stirring shafts.
In recent years, along with the increasing demand for a more compact image formation apparatus, the reduction in the height (depth) of the casing of a developing apparatus has been strongly demanded from the viewpoint of space saving. Due to the constraint of the installation inside the developing apparatus, the casing is expanded to the lateral direction in order to secure a necessary volume of a developer. Alternatively, the size of developer stirring shafts is reduced, or pluralization of developer stirring shafts is enhanced.
However, when the developing apparatus is formed in a small height, there is a problem that the performance becomes influenced due to the slanting, and an influence of uneven stirring tends to occur. Further, there has been a problem that the conveying and the stirring performance of the developer are lowered.
Further, all the structures disclosed in the above publications are designed for application to the conventional developing apparatuses having a general depth of the development casing, and are not designed for the above-described developing apparatus having a small height. Therefore, the developing apparatus having a small height are easily affected by environmental disturbances, and cannot provide a stable supply of the developer to the development roller. Thus, there has been a problem that it is not possible to avoid a reduction in the conveying performance and the stirring performance of the developer.
The present invention has been made in view of the above-described conventional problems. It is, therefore, an object of the present invention to provide a developing apparatus that uses developer stirring shafts in a simple structure, that keeps a volume balance of the distribution of a developer in the axial direction within a development casing, that can improve the efficiency of the stirring of the developer without receiving an influence of an inclined disposition of the development casing, and that optimizes the supply of the developer to a development roller.
In order to achieve the above object, the present invention is configured as follows.
According to a first aspect of the present invention, a developing apparatus that is equipped with a development casing that serves as a developing tank by storing developer, a development roller that supplies the developer within the development casing to a developing section, and a plurality of developer stirring shafts that rotate together with the development roller, thereby to stir and convey the developer within the development casing based on the rotation of the developer stirring shafts, and characterized in that the plurality of developer stirring shafts are disposed mutually adjacent to each other and are also disposed substantially in parallel with the development roller, and each developer stirring shaft has a rotational axis that rotates together with the development roller and having a plurality of stirring vanes of an approximately elliptic shape laid out at a predetermined angle with respect to the rotational axis, wherein the stirring vanes being disposed substantially in parallel with each other, with the opposing stirring vanes between the adjacent developer stirring shafts having mutually different installation positions in the axial direction.
Further, according to a second aspect of the present invention, a developing apparatus of the first aspect is further characterized in that the stirring vanes that are adjacent in the axial direction of the rotational axis are disposed with substantially equal intervals.
Further, according to a third aspect of the present invention, a developing apparatus of the first aspect is further characterized in that, between the adjacently disposed developer stirring shafts, the stirring vanes are installed in the axial directions in such a way that the tip portions of the stirring vanes of one developer stirring shaft oppose substantially the center positions of gaps formed between the tip portions of the stirring vanes of the other developer stirring shaft.
Further, according to a fourth aspect of the present invention, a developing apparatus of the first aspect is further characterized in that, between the adjacently disposed developer stirring shafts, the stirring vanes are installed in the axial directions in such a way that the stirring vanes are positioned by sequentially shifting the installation positions by the amount of (the distance between the adjacent stirring vanes/the number of the developer stirring shafts).
Further, according to a fifth aspect of the present invention, a developing apparatus of the first aspect is further characterized in that the developer stirring shafts that are positioned in odd-number rows counted from the development roller are each set to have a number of stirring vanes that is different from the number of stirring vanes of each of developer stirring shafts that are positioned in even-number rows counted from the development roller, and the stirring vanes of the developer stirring shafts that are located at positions in the order of odd numbers of developer stirring shafts counted from the position of the development roller are set to have all the same shapes, and the stirring vanes of the developer stirring shafts that are located at positions in the order of even numbers of developer stirring shafts counted from the position of the development roller are set to have all the same shapes.
Further, according to a sixth aspect of the present invention, a developing apparatus of the first aspect is further characterized in that, between the plurality of developer stirring shafts laid out in parallel with each other, a difference in the moving speeds of the tip portions of the stirring vane is set to within xc2x120%.
Further, according to a seventh aspect of the present invention, a developing apparatus of the first aspect in further characterized in that, in each of the developer stirring shafts, stirring vanes are disposed symmetrically around a vertical direction with respect to an axial direction with the center of the developer stirring shaft as a boundary, and, between the adjacent developer stirring shafts, the installation positions of the stirring vanes in the axial direction are shifted by half pitch each.
Further, according to an eighth aspect of the present invention, a developing apparatus of the first aspect is further characterized in that in each of the developer stirring shafts, stirring vanes are positioned with gradually decreasing intervals between adjacent stirring vanes starting from the center of the developer stirring shaft as a boundary toward both ends.
According to the above first aspect, the plurality of developer stirring shafts are disposed mutually adjacent to each other and also in parallel with the development roller. Each developer stirring shaft has a plurality of stirring vanes of an approximately elliptic shape laid out at a predetermined angle with respect to the rotational axis. The stirring vanes are disposed substantially in parallel with each other. Further, the opposing stirring vanes between the adjacent developer stirring shafts have mutually different installation positions in the axial direction. Based on this structure, between the adjacent developer stirring shaft, maximum as well as minimum points of stirring and conveying force are not overlapped with each other. Therefore, it is possible to make uniform the force of stirring and conveying the developer in the axial direction of the developer stirring shafts. As a result, it is possible to stabilize the stirring of the developer, and to achieve uniform conveyance of the developer.
Further, according to the second aspect, the developer is disposed uniformly between the stirring vanes. As a result, it is possible to improve the stabilized stirring of the developer, and to improve the uniform conveyance of the developer.
Further, according to the third aspect, the gap portions of the stirring vanes that have weak conveying force of the developer and that are formed by the adjacent stirring vanes oppose the tip portions of the stirring vanes that have strong conveying force of the developer. Therefore, the large conveying force at the tip portions of the stirring vanes of one developer stirring shaft can compensate for the weak conveying force at the gap portions of the stirring vanes of the other developer stirring shaft. As a result, the peak and bottom at the interface of the developer becomes rather insignificant, and it becomes possible to suppress the generation of the uneven stirring during the development.
Further, according to the fourth aspect, it is possible to avoid the overlapping of maximum as well as minimum points of stirring and conveying force, by sequentially shifting the installation positions of the stirring vanes of the adjacent developer stirring shafts. Therefore, it is possible to gradually suppress the fluctuation in the stirring and conveying conditions of the developer depending upon positions where stirring vanes are present or not. As a result, it is possible to suppress the generation of the uneven stirring of the developer.
Further, according to the fifth aspect, even when the number of developer stirring shafts of the developing apparatus is required to be increased or decreased, it is possible to cope with the situation by using the developer stirring shafts of two different kinds of shapes. As a result, it is possible to minimize the number of the kinds of machine parts.
Further, according to the sixth aspect, it is possible to make substantially the same the moving speeds of the tip portions of the stirring vane of each developer stirring shaft. As a result, it is possible to provide a stable supply of the developer necessary for the development to the developing section.
Further, according to the seventh aspect, when the stirring vanes are disposed in symmetry with the center of the developer stirring shaft in the axial direction as a boundary, the developer flows from the center portion to both ends within the development casing. Therefore, it is possible to suppress the maldistribution of the developer. At the same time, the developer is stirred toward both ends of the axial direction of the developer stirring shaft. As a result, it is possible to make uniform the distribution of the developer at both ends.
Further, according to the eighth aspect, as the interval between the stirring vanes becomes smaller toward both ends of the developer stirring shaft, the holding of the developer by the stirring vanes is increased. As a result, there is an effect that there is less influence of the shape of the development casing or the installation inclination.
While the above explains the aspects of the present invention, it is needless to mention that a suitable combination of these aspects belongs to the scope of the present invention.